Hydroaccumulators with separating elements are used preferably in hydraulic systems, among others for energy storage, for emergency actuation of overall hydraulic systems, shock absorption, etc. The hydroaccumulators are by definition considered pressure vessels, by a certain useful volume being storable depending on the application. Ordinarily hydroaccumulators with a separating element are differentiated into bladder accumulators, membrane accumulators and piston accumulators, the manner of action being based on the compressibility of the working gas used for fluid storage. Generally nitrogen is used as the working gas. The separating element divides hydropneumatic accumulators into a gas part and into a liquid part, the latter being connected to the hydraulic circuit. When the pressure on the fluid side rises, the gas on the gas side is compressed in the gas chamber. When the pressure drops on the fluid side, the compressed gas can expand and displace the stored liquid in the accumulator back into the hydraulic circuit.
Since the separating element in the form of a membrane of elastomer material is generally subject to a certain gas permeability, especially with longer use of the hydroaccumulator, the working gas can diffuse through the separating membrane onto the fluid side of the accumulator and be lost. The working capacity of the hydroaccumulator then continuously decreases. To counteract this loss of working capacity in bladder accumulators, the gas side of the accumulator is designed especially for the connection of pressure vessels. Through a pipework as the connection, the gas side of the hydraulic bladder accumulator is permanently connected to carry gas to the pressure vessel which is then used as a gas refilling means for the respective working gas, preferably in the form of nitrogen. Fundamentally, gas is not actually rerouted into the hydroaccumulator through the gas refilling means. Rather, the gas volume is added by the addition of the volume of the gas chamber in the accumulator and of the gas chamber in the pressure accumulator so that partial gas losses by diffusion through the separating membrane become less important relative to the total volume of the stored working gas. The service life of the hydraulic bladder accumulator can then be prolonged. Moreover, the pressure rise at the same displaced liquid volume is less.
In practice, the approaches made in this respect, as a result of the separate arrangement of the hydroaccumulator and the pressure vessel as the gas refilling means, require a large amount of installation space. The existing pipework as the connecting means between the containers generally has leaks. Inherently, the advantage desired by the additional gas refilling means is at least in part lost again by the leaks. Furthermore, the pipework can only be produced as a permanently gas-carrying connecting means between the containers so that not only do production costs arise due to the pipework itself, but other costs due to installation efforts also arise.
This bladder accumulator with permanently connected gas refilling means has the separating membrane made as a gas bladder. The bladder is filled by a gas valve located on the top part of the hydroaccumulator and connected as part of the connecting means opened to the pipework, and accordingly to the gas refilling means. As a result of the large volume pressure vessel used as the gas refilling means, this configuration has generally only been used in large-volume hydroaccumulators, such as bladder accumulators, or in piston accumulators in which the separating element is a sealed separating piston movable within the accumulator housing. In the piston accumulator, the diffusion of gas toward the fluid side takes place through the sealing means on the outside periphery of the separating piston which slides along the inner peripheral side of the hydroaccumulator housing for the working process of the accumulator.